Hi,

What lens are you encountering this problem with?

I've read where photographers use a pencil eraser to clean the contacts on the lens to eliminate this problem.

I bought a EOS 10D 2 years ago hoping to use my older Canon lenses. I kept getting the err99 at random. I purchased a used Sigma 70-200 lense and the problem became worst. I contacted Sigma and they were aware of the problem with Canon and offered a free chip upgrade. I took the lense in in person and the upgrade was done within minutes. Never had the problem since. I purchased a 28-110 Canon lense and have never experienced the problem. I don't think this is what you want to hear but my frustrations are now gone...

I bought a used Canon 10D and got the same error message after playing around in the menu and connecting an old canon lens (4+years old). I tried another lens that had worked prior to the error with no luck. I then took out the batteries (the main and the date/data battery) and let the camera sit for about 1 minute with no power source. Then I reinstalled the batteries and it worked fine. No more error code, even with the lens that previously did not work.